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Re: Syntarsus



T. Mike Keesey asks:
 
>  > It seems like Syntarsus is a paraphyletic species, with S. kayentakatae
>  > closer to Dilophosaurus than to S. rhodesiensis! Is this the case?

Stan Friesen replies:
 
> Probably not.  Crests are dratted poor characters to use for phylogenetic
> analysis.  They tend to change rapidly, and unpredictably, and certainly
> evolved many times in Theropoda.

I'll have to disagree with Stan on this point.  Even though both S. 
rhodesiensis and S. kayentakatae possess an extra opening in the 
upper jaw, I've never been convinced that both belong to the same 
genus.  I think Syntarsus is paraphyletic, with S. kayentakatae 
closer to Dilophosaurus than S. rhodesiensis.

True, cranial crests of one shape or another pop up in various 
theropod crests.  But _paired nasolacrimal crests_ are found in only 
two (possibly three) species that I know of, and all are coelophysoids 
- Dilophosaurus wetherilli, Syntarsus kayentakatae, and (rumour has 
it) one of the Ghost Ranch theropods, possibly a Syntarsus species.  

Paired nasolacrimal crests is quite an elaborate character, and one 
that I don't believe evolved more than once in ceratosaur evolution.  
Therefore, I think it's a useful synapomorphic character.  

S. rhodesiensis does not belong to Coelophysis.  S. kayentakatae 
deserves its own genus.  As for Liliensternus liliensterni, I'm not 
too sure where it sits in coelophysoid evolution.

Tim Williams